Image vignetting refers to an effect where border areas of an image, particularly the corners, are darker relative to the center of the image. Vignetting is typically caused primarily by inherent design characteristics of lenses, which result in an uneven distribution of light upon the optical plane (e.g., film or image sensor) of a camera. Wide angle lenses and digital zoom lenses, especially at wider apertures, often create high levels of vignetting. Depending on the level, vignetting can be very noticeable and distract from the quality of the image. This is particularly true when creating a single panoramic image from one or more individual images, where vignetting causes the borders between the individual images to be darker than other areas of the image, resulting in the panoramic image having a “striped” appearance.
Vignetting can be automatically corrected when parameters associated with formation of the image (e.g., lens type, focal length, aperture settings, etc.) are known. However, such information is often not available for images. Several techniques have been developed for vignette correction, however, most involve comparison between multiple images from a moving camera. For example, one technique involves comparing the intensity of a same object in different images from a moving camera, wherein the object is located at a different position relative to the image center in each image. Vignetting correction is determined based on differences in intensity of the object between the two images.
While generally effective at correcting vignetting when multiple images from a moving camera are available, such techniques are not effective at correcting vignetting in multiple images from a camera having little or no motion, and are not applicable to correcting vignetting in a single image.